1. Field of the Invention
The invention relates to a method for compensating for a position error in an optical disc apparatus, and, more particularly, to a method for compensating for a position error generated when a label is printed on a label surface of an optical disc by an optical disc apparatus.
2. Background of the Related Art
Optical discs have been developed recently which allow data to be recorded on a data surface of the disc, and a label with a desired design to be printed on the opposite, or non-data surface of the disc. The surface of the disc on which a label is printed is referred to as the label surface of the disc. Labels are typically transferred onto the label surface of the disc using a laser etching technology commonly referred to as LightScribe, in which a laser burns or etches an image onto a specially prepared, non-data side of an optical disc. A LightScribe disc is referred to herein simply for ease of discussion. However, it is well understood by those of ordinary skill in the art that the invention may be applied to any such disc which includes a surface on which a label may be printed, and, more particularly, to any such disc which includes a data side and a non-data side which has been specially prepared for laser printing or etching.
A land/groove for performing a tracking servo operation during a data recording process is formed on the data surface of the optical disc, and Absolute Time In Pre-groove (ATIP) information for detecting a current position is recorded as a wobble land/groove. An optical disc recording apparatus receives a push-pull signal generated by the land/groove and performs a tracking servo operation using an established feedback scheme, recognizes a current position based on the ATIP information, and thus can perform a random access operation at a desired position.
However, such a wooble land/groove is formed only on the data surface of the disc, and not on the label surface of the disc. Thus, as the label surface lacks the ATIP information used to detect a current position, neither the tracking servo operation nor the random access operation can be performed on the label surface of the disc. Rather, labels must be sequentially printed on the label surface of the optical disc, starting at an inner area and progressing towards an outer area of the optical disc based on a feed-forward scheme. Thus, this type of disc is very sensitive to the dynamic characteristics of an actuator of the optical pickup unit associated with a tracking servo.
To address these problems, a saw-teeth zone is allocated to a Control Feature Outer Ring (CFOR) zone of this type of disc. The CFOR zone is provided on the label surface in the form of a circular band having a predetermined width of, for example, 650 μm. Other widths may also be appropriate. The saw-teeth zone is divided into two zones opposite each other in the CFOR zone in consideration of eccentricity of the optical disc. A first area having a high reflection factor engages with a second area having a low reflection factor in the form of a plurality of saw-teeth. As a laser beam is directed at the center of the CFOR zone and the disc rotates, a resulting duty ratio of a reflected signal should be 50%. However, if a predetermined voltage is applied to an actuator arranged in the direction of a track which causes an objective lens to be positioned off center of the CFOR zone, as the disc rotates a laser beam directed at the CFOR zone is also off center, and the resulting duty ratio of the reflected signal would not necessarily be equal to 50%.
Therefore, an optical recording apparatus capable of performing a label-printing operation on a label surface of a disc may measure an actual sensitivity the actuator as it moves the objective lens in a track direction based on the magnitude of a predetermined voltage to be applied to the actuator in order to shift an objective lens to the outer area of the disc by a predetermined distance, and then perform a tracking servo operation using a feed-forward scheme based on the measured actual sensitivity of the track-direction actuator. However, other critical components associated with this tracking servo operation which affect recording quality of the optical disc include the dynamic characteristics of a sled motor which moves the optical pickup unit in a radial direction of the disc. The sled motor includes a step motor and a device for converting a rotation of the step motor into rectilinear motion. This conversion often results in unexpected step errors generated by mechanical factors (such as, for example, angle errors in frame/yoke values, non-uniform assembly at an inner diameter of the frame/yoke values, and the like) and electrical factors (such as, for example, winding resistance, non-uniformity between inductance phases, and unbalanced magnetic flux formed on the surface of each tooth, and the like).
FIG. 1 shows an ideal sled movement distance and actual sled movement distance for each step of an exemplary step motor. Due to the above-mentioned factors, an unexpected position error may occur during the sled movement as shown in FIG. 1. The tracking error resulting from this position error is shown in FIG. 2. Therefore, although the optical recording apparatus capable of performing a label-printing operation may be able to compensate for dynamic characteristics of an actuator based on operation of the saw-teeth zone, it cannot compensate for any position error generated by the sled motor as the optical pickup unit moves from the inner portion towards an outer circumference of the disc. This position error may result in space on the label surface on which a portion of a label is not printed may, or a portion of a label may be printed twice, each resulting in deterioration of quality.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.